A humidity adjustment device described in Patent Literature 1 includes two heat exchangers. Each of the heat exchangers has an adsorbent fixed to it, which, at temperatures equal to or lower than a predetermined temperature, performs an adsorption action of absorbing water, and once the predetermined temperature is exceeded, starts a regeneration action by releasing the water. In the humidity adjustment device, the outside air is forced into the inside of the room through one of the heat exchangers, while the room air is exhausted to the outside of the room through the other heat exchanger. Since the temperature is equal to or lower than the predetermined temperature when the heat exchanger acts as an evaporator, it performs the adsorption action and fulfills a dehumidification function. On the other hand, since the temperature is equal to or higher than the predetermined temperature when the heat exchanger acts as a condenser, it performs the regeneration action and fulfills a humidification function. Accordingly, when the room is to be humidified, the outside air is passed through the heat exchanger acting as the condenser before it is supplied to the inside of the room. When the room is to be dehumidified, the outside air is passed through the heat exchanger acting as the evaporator before it is supplied to the inside of the room.
At the time of startup of the humidity adjustment device, in order to measure the outside air temperature and the room air temperature, a fan is driven to force the outside air and the room air into the humidity adjustment device. At this point, if the temperature of the air passing through the evaporator is excessively low, an amount of a refrigerant resulting from liquefaction of the evaporated refrigerant in the evaporator becomes larger. If the compressor is started in this condition, an excessive amount of the liquid refrigerant is sucked into the compressor, making it difficult for an accumulator to completely separate the gas and the liquid. This can result in the liquid refrigerant returning to the compressor. It is therefore necessary to suppress the return of the liquid refrigerant which occurs at the time of startup of the humidity adjustment device.